The detection of pathogenic microorganisms in biological fluids should be performed in the shortest possible time, in particular in the case of septicemia for which the mortality remains high in spite of the broad range of antibiotics which are available to doctors. The presence of biologically active agents such as a microorganism in a patient's body fluid, especially blood, is generally determined using blood culture bottles. A small quantity of blood is injected through an enclosing rubber septum into a sterile bottle containing a culture medium, and the bottle is then incubated at 37° C. and monitored for microorganism growth.
Instruments currently exist on the market in the U.S. that detect the growth of a microorganism in a biological sample. One such instrument is the BacT/ALERT® 3D instrument of the present assignee bioMérieux, Inc. The instrument receives a blood culture bottle containing a blood sample, e.g., from a human patient. A byproduct of microbial growth is generation of carbon dioxide gas within the bottle. Inside the bottle, mounted onto the bottom surface, is a sensor that changes color with increasing concentrations of carbon dioxide gas. The instrument incubates the bottle and periodically during incubation an optical detection unit in the incubator analyzes the sensor to detect whether microbial growth has occurred within the bottle. The optical detection unit, bottles and sensors are described in the patent literature, see U.S. Pat. Nos. 4,945,060; 5,094,955; 5,162,229; 5,164,796; 5,217,876; 5,795,773; and 5,856,175, the entire content of each of which is incorporated by reference herein. Other prior art of interest relating generally to the detection of microorganisms in a biological sample includes the following patents: U.S. Pat. No. 5,770,394, U.S. Pat. No. 5,518,923; U.S. Pat. No. 5,498,543, U.S. Pat. No. 5,432,061, U.S. Pat. No. 5,371,016, U.S. Pat. No. 5,397,709, U.S. Pat. No. 5,344,417 and its continuation U.S. Pat. No. 5,374,264, U.S. Pat. No. 6,709,857; and U.S. Pat. No. 7,211,430, the entire content of each of which is incorporated by reference herein.
Agitation of the bottles in the BacT/ALERT instrument during incubation is one of the features of the instrument in order to accelerate bacterial growth. Existing blood culture detection systems configure the agitating racks assemblies either into drawers or stack them vertically behind a door. The drawers orient the racks lengthwise to the user to minimize instrument space. Opening the drawers exposes the samples to ambient air temperature which can slow bacterial growth and increase the detection time. Arranging the racks behind a door improves temperature control but results in a significantly larger instrument.